A channel inductor is an electric device for melting and holding of metal. The inductor comprises a first primary winding, e.g. a multi-turn coil wound around a magnetic core. Around this core and the coil is a channel, normally called inductor channel, arranged. The channel opens at both its ends into a furnace vat. The inductor and the channel is normally contained in a removable inductor housing such that the inductor can be replaced without the need to reline the complete furnace vat.
The inductor channel, which during operation is filled with molten metal, constitutes a closed circuit. As the primary winding during operation is fed with an alternating current the melt in the inductor channel acts as a short-circuited secondary winding of a transformer. Power is thus induced in the melt which is heated and a flow pattern is developed in the channel. Due to the good stirring effect provided by the inductor a good homogenization as to temperature and composition will be achieved in the melt rendering this type of furnace suitable for many type of refining and alloying treatments. However the flow pattern generated in the channel, which normally is a two-loop flow over the channel cross-section, might also create erosion of the lining in the inductor or in some cases deposition of refining agents, solid particulate matter formed in the melt or other particles on the walls in the inductor channel resulting in a clogging of the channel. Such clogging will disturb the flow in the channel and thus the efficiency of the inductor.
A channel inductor is normally equipped with a cooling jacket for cooling of both the housing and the coil. The cooling jacket is arranged within the refractory lining provided around the coil, i.e. between the coil and the inductor channel and will shield the coil from any moisture given off by the lining material during sintering of the lining but will also constitute a protective barrier or shield around the coil which any melt which happens to penetrate the lining have to pass. The cooling jacket will, however, cause substantial thermal and electric losses. These losses will show as the heating of the water passing through the cooling jacket. Today refractory lining is normally applied as dried masses which are formed around templates without any water-additions. As the masses contain essentially no added water and there is no longer a need to protect the coil from moisture in the refractory lining and the primary object of the cooling jacket is in installations using this type of linings to protect the coil from any metal penetrating through the lining. Thereby has it become advantageous to design a channel inductor without the cooling jacket, giving the following advantages;
the inductive losses to the cooling jacket are eliminated; PA1 possibility to reduce the thermal losses by an increasing the distance from the hot melt to the cooling system comprised in the coil; PA1 possibility to increase the overall efficiency of the inductor; PA1 possibility to increase melt and/or superheat capacity; and PA1 reduced maintenance as the corrosion situation in the cooling jacket is eliminated as will all water couplings etc. and supply hoses or tubes for the cooling jacket. PA1 the width of the channel which exhibits an essentially oval or rectangular cross-section with a width to radial height ratio of 1.5 or larger; PA1 the radial height shall vary along the channel; PA1 and preferably shall the inner-wall of the channel in area between the two openings of the inductor channel show an angle across half the channel width that is 0 degrees at the openings and at least 30 degrees at a center point between the openings. A channel designed according to these criteria will exhibit an improved flow with essentially no zones of stagnation and dead-water in a cross-section at any point along the channel. Preferably the variation of the radial height shall comprise sectors where the height is increased alternating with sectors where the height is decreased. The change in relative height along the channel will along the whole channel length both exhibit sectors with increasing radial height and sectors with decreasing radial height. The changes shall over such a sector correspond to a change of the radial height with at least 25% within a sector of one-eight of the periphery of the channel. As essentially all zones of stagnation or dead-water is eliminated in the cross-section flow pattern in the channel the deposition and clogging is substantially reduced. The changes in the cross-section flow pattern will also substantially reduce wear.
The inductor and especially the coil must however be safe-guarded against melt penetrating through the lining and damaging the coil and also against excessive wear especially in cases with increased superheat or melt capacity which are likely to increase the temperature in the interface melt/refractory lining and possible also the flow rate in the inductor channel. It is also an object to reduce the thermal and mechanical stresses, which the lining around the coil is subjected to.
It is therefore the object of the present invention to provide a channel inductor with an improved thermal efficiency and reduced need for maintenance while maintaining or improving the operational safety. It is one object that the cooling jacket shall be removed but that the inductor still shall be safe guarded from damage to the coil due to metal penetration. That is any metal penetration shall be prevented to reach the inductor coil. Further it is also an object to improve the flow characteristics of the inductor channel to reduce wear and to improve the control of supplied electrical power to reduce depositions and clogging and also measures will taken reduce losses to the mechanical structure and cooling system.